A rotary drilling jar is set forth in earlier U.S. Pat. Nos. 3,208,541 and 3,233,690 issued to Richard R. Lawrence. The rotary drilling jar set forth in those patents has met with substantial acceptance around the world. It is a jar which is typically installed in a drill stem normally incorporating a drill bit at the bottom, various drill collars thereabove, stabilizers as necessary, and a plurality of drill pipe to extend from the kelly at the derrick to the bottom of the borehole. Typically, the drill stem includes the drill bit at the bottom with several collars or stabilizers or both just above the drill bit. In typical operations, the drill pipe is substantially smaller in diameter than the drill collars. As an example, 8 inch drill collars may be mounted above a drill bit of 91/2 inches, and the remainder of the distance to the derrick will be fabricated from a string of 41/2 inch diameter drill pipe. The drill stem is filled with drilling mud of substantial weight. The weight on bit may readily approach 100,000 pounds in a well of about 15,000 feet. The drill stem is normally rotated at a speed of about 35 to 150 rpm by a rotary table engaging the kelly, a non-round member of the drill stem.
In a drill stem of this typical size, it is possible for the drill bit to drill a crooked hole, thereby forcing the drill collars just above the bit against the side wall. It is possible to stick the drill stem. If sticking occurs, it typically happens near the drill collars where they keyseat the crooked hole and are held against the side wall of the hole. When the drill stem is stuck, it is possible to lose a part of the drill stem by twisting off at some point above the point where sticking occurred, necessitating a fishing job to clear the borehole of the broken drill stem.
To prevent the foregoing, it is appropriate to incorporate a drilling jar typified by this disclosure in the drill stem at the lower end of the drill pipe and just above the drill collars and stabilizers or partially below the drill collar. A drilling jar is typically included; this is a device which can be latched and then released to enable its components to telescope. On actuation, components known as a hammer and anvil are struck together to deliver a jar or jolt to the drill stem. This hammering action can be controlled and occurs upwardly or downwardly. It is intended to break the stuck drill stem free at the place where it is stuck.
The rotary drilling jar, when operated, is moved in a telescoping fashion. It is exposed to drilling mud. Drilling mud is a liquid weight material pumped through the drill stem and returned on the annular space on the exterior. Small particles of drilled formation debris and the like are carried in the annular space. Conventional rotary drilling jars are normally secured together by means of a latch mechanism between the major components of the drilling jar. Pressures in the vicinity of the drilling jar are quite high, typically in the range of 1,500-5,000 psi. Drilling jars constructed in accordance with the teachings of the two mentioned United States patents have an annular cavity within. This cavity is filled with drilling mud in ordinary operation. The mud is laden with particulate trash which will abrade and damage the drilling jar. The references mentioned above disclose encircling rings which define the annular cavity or chamber within the drilling jar. As the jar is axially operated, this chamber or cavity is changed in size. This requires the drilling mud to flow quickly into or out of the chamber, depending on the direction of stroke. This annular chamber, defined at one end by encircling resilient rings, operates as a fluid damping chamber. This may slow down operation of the tool.
As set forth in application Ser. No. 203,527 which was filed Nov. 3, 1980, now issued and bearing U.S. Pat. No. 4,394,883, resilient parallel snubbers are shown. The snubbers enlarge the narrow passage into or out of the annular cavity or chamber. Several parallel resilient snubbers are installed as set forth in that patent, thereby permitting more rapid flow through the narrowed passage. The flow characteristic is improved; additionally, the resilient snubbers improve damping of vibration. It will be understood that the climate where the drilling jar is used is extremely hostile. This is all the more so in light of the fact that recent wells are deeper, thereby placing greater loads on the drill stem. Elongate parallel vibration dampers are set forth in the referenced patent. They are mounted with a plurality of screws. It is important to mount them in fixed fashion, a set of such resilient vibration dampers protecting the reciprocating components of the drilling jar. However, servicing limitations and the time required to assemble or disassemble such vibration dampers make the construction of this disclosure quite attractive. This construction enables the vibration dampers to be mounted individually and with great ease and facility. They are installed in undercut grooves. This enables several to be installed quickly, all terminating at the end of the respective grooves in which they are positioned. Moreover, they are well fastened, secured, and not readily torn free by the vigorous use that is inevitably encountered. An entire set of vibration dampers can be removed and replaced with a new set of vibration dampers in quick order through the use of the present invention.
This invention is a improvement over the structure shown in the referenced patent. It is an improvement in that it enables the vibration dampers to be installed quickly and easily and with greater certainty. Hand labor is reduced. The risk of stripping threads is eliminated.
From the foregoing, the present disclosure is summarized as a device enabling the mounting and demounting of plurality of parallel resilient vibration dampers in undercut grooves. All the grooves are parallel to one another, extending from a neck of reduced diameter to enable easy insertion. The neck fully encircles the device, thereby receiving a C-shaped lock ring which is spread by means of a tapered surface immediately adjacent to the neck. The lock ring secures the resilient dampers in position.